Blender 2.8 doesn't recognize my graphics card for GPU
Blender is only capable of doing GPU rendering on CUDA (NVIDIA cards) and openCL (originally develop by Apple &amp; maintained by Khronos group)(1). However Mac dropped support for openCL(2) therefore there is no way to use an AMD GPU for GPU rendering on Blender nor other software that uses only openCL.

The only option, that I haven't tested is to try to use Linux on your machine and download AMDGPU-PRO from AMD's website. No guaranteed to work.

1.- GPU Rendering - Blender Manual

2.- Apple Drops OpenGL and OpenCL